Modeling user preferences from users' historical sequences is one of the core problems of sequential recommendation. Previous studies only considered transition patterns between user-items, ignoring transition patterns between item features and item-item interactions. Recently, there has been interest in integrating knowledge graphs as auxiliary information into sequential recommendation. Most of the existing methods deal with the heterogeneous information in the knowledge graph in a coarse-grained manner. We believe that fine-grained processing of information in knowledge graphs can help recommendation systems understand changes in user preferences, i.e. dividing hetero-geneous information into item-to-item relationships and item-to-attribute relationships. In this paper, we propose a dual-level self-attention network for sequential recommendation. Specifically, we divide the knowledge graph heterogeneous information about items into relation level and attribute level, representing item-item relationship and item-attribute relationship, respectively. Afterwards, the self-attention network is used to learn user preferences at dual-level, respectively. Then, the outputs of the above dual levels are integrated for next item recommendation. Based on extensive experiments on three real-world data sets, our model achieves significant improvements compared to state-of-the-art baseline methods.